Mid Sweden University

The photosynthetic and respiratoric capacity of Fucus vesiculosus grown at three different levels of salinity (4.5, 8 and 20‰) was studied in the presence of different concentrations of lead (5, 10, 15, 20, 25, and 30 mg PbCl₂ L^-1). The studies were performed by using a light-pipette, which has a precisely defined light source of photosynthetic active radiation (PAR, 400-700 nm). The photosynthetic and respiratoric capacity of the algae were measured when exposed to light pulses with increasing irradiance and after 24 hr in seawater with the addition of lead. The results indicate that the photosynthetic capacity of F. visiculosus from 20‰ is more sensitive to lead compared to those from 8 and 4.5‰. The photosynthetic capacity was reduced by 69% at 30 mg PbCl₂ L^-1 compared to the control alga. The photosynthetic capacity of F vesiculosus from 8 and 4.5‰ was reduced by 38 and 15%. The respiratoric capacity of F. vesiculosus from 20‰ was reduced by 41% at 30 mg PbCl₂ L^-1. However, the respiratoric capacity of the algae from 4.5‰ increased by 55% at the same concentration of PbCl₂. The results indicate that lead showed inhibitory effects on photosynthesis but a stimulatory effect on respiration of F versiculosus grown at low levels of salinity.

Fucus vesiculosus from the northern Baltic Sea (5 psu) and from the Irish Sea (35 psu) were cultivated at different temperatures, salinities and dissolved inorganic carbon (DIC) concentrations with the addition of different nutrient concentrations. The influence of these abiotic factors was assessed by measuring photosynthesis as electron transport rate (ETR) and growth as relative growth rate (RGR). The maximal ETR and the RGR of the Irish Sea plants in their natural seawater (50.8 mol electrons m(-2) s-1; 0.024 g g(-1) day(-1)) were significantly higher than those of the Baltic plants in their natural seawater (21.9 mol electrons m-2 s(-1); 0.007 g g(-1) day(-1)). When Baltic F. vesiculosus was cultivated at a DIC concentration similar to that of the Irish Sea, the ETR as well as RGR increased, but never equalled the rates of the marine F. vesiculosus from the Irish Sea. Cultivation at different salinities showed that F. vesiculosus from the Baltic has a higher ETRmax and RGR at low salinities (5-10 psu) than F. vesiculosus from the Irish Sea, whose ETR and RGR decreased sharply in salinities below 20 psu. Plants from both sites grown at high nutrient concentrations, however, performed better at low salinities than those grown under low nutrient conditions. Salinity had the greatest impact on differences in ETR and RGR between the two populations, followed by differences in DIC and nutrient concentrations. There was a highly significant correlation between ETRmax and RGR in plants from both sites and across the full range of culture conditions, indicating that the same amount of energy from photosynthesis is used for growth in both varieties of the species at different salinities. The photosynthesis of F. vesiculosus in the northern Baltic is close to the minimum demand for growth, which may account for their small size. The temperature optimum for F. vesiculosus from the Baltic was 4-10 degrees C, while that for F. vesiculosus from the Irish Sea was 15-20 degrees C. The photosynthesis of Irish Sea plants was less strongly affected by exposure to high irradiances than that of plants from the Baltic.

Cadmium (Cd) uptake capacities and Cd tolerance of the marine alga Fucus vesiculosus from the Irish Sea (salinity 35 psu) and from the Bothnian Sea (northern Baltic, 5 psu) were quantified. These data were complemented by measurements of changes in maximal photosynthetic rate (Pmax), dark respiration rate and variable fluorescence vs. maximal fluorescence (Fv:Fm). At concentrations between 0.01 and 1 mmol Cd l−1, F. vesiculosus from the Bothnian Sea adsorbed significantly more (about 98%) Cd compared with F. vesiculosus from the Irish Sea. The photosynthetic measurements showed that the Bothnian Sea F. vesiculosus were more sensitive to Cd exposure than the Irish Sea algae. The algae from the Irish Sea showed negative photosynthetic effects only at 1 mmol Cd l−1, which was expressed as a decreased Pmax (−12.3%) and Fv:Fm (−4.6%). On the contrary, the algae from the Bothnian Sea were negatively affected already at Cd concentrations as low at 0.1 mmol Cd l−1. They exhibited increased dark respiration (+11.1%) and decreased Fv:Fm (−13.9%). The results show that F. vesiculosus from the Bothnian Sea may be an efficient sorption substrate for Cd removal from Cd contaminated seawater and this algae type may also have applications for wastewater treatment.